The term 'PART OF DOS' can be broken down into four crossword solutions: SYST (4 letters), SYSTEM (6 letters), DISK (4 letters), and SYS (3 letters). The acronym DOS stands for DISK Operating SYSTEM, which is a type of operating SYSTEM that was used in the 1980s and 1990s. SYST, SYSTEM, and SYS are all related to DOS, as they refer to the SYSTEM files that are part of the DOS operating SYSTEM. DISK refers to the physical storage device that holds the DOS SYSTEM files.